Yuanzineng kexue jishu (Jun 2023)
Preparation and Property of Palladium/Alumina Composite
Abstract
Palladium is often used as the preferred material for hydrogen isotope separation, but pure palladium tends to be pulverized due to internal stress after repeated hydrogen absorption and desorption cycles. The pulverized palladium particles will increase hydrogen flow resistance, and even block the whole separation system in serious cases, thus affecting the separation efficiency and stability. In order to find suitable materials for hydrogen isotope separation, Pd/Al2O3 composite with 40.1% (mass fraction) palladium content was prepared by impregnation-reduction method using porous alumina as carrier and PdCl2 solution as palladium precursor. X-ray diffraction (XRD), BET surface area measurement, transmission electron microscope (TEM), and energy dispersive X-ray spectroscopy (EDS) techniques were used to study the phase, specific surface area and pore size distribution, morphology and composition of the material. The kinetics and thermodynamic properties of hydrogen absorption and desorption, hydrogen absorption and desorption cycling properties and anti-pulverization properties were tested by the volumetric absorption/desorption apparatus. Phase analysis results show that the alumina carrier exists in amorphous structure, the supported palladium particles have good crystallinity, and the precursor palladium is fully reduced without introducing other impurities. The results of specific surface area and pore size analysis show that most of the pores in the alumina carrier are mesoporous, the supported palladium exists in the pores of the Al2O3 carrier, and the Al2O3 carrier can bear a higher amount of palladium. The morphology analysis show that the palladium particles are well dispersed and the size range is from 8 nm to 50 nm. The hydrogen storage performance tests show that compared with the pure palladium, the maximum hydrogen capacity of Pd/Al2O3 composites is about 95% of the pure palladium, the plateau pressures of absorption and desorption increase by 21% and 12% separately, and the slope of absorption/desorption plateau increases. The hydrogen absorption rate is 5 times higher than that of pure palladium. It is speculated that the large specific surface area of nanocrystalline palladium particles increases the contact area with hydrogen, and the grain boundaries of nanocrystalline palladium particles provide more diffusion channels and reduce diffusion distance for hydrogen atoms. After 2 000 cycles of thermo induced hydrogen absorption and desorption, the hydrogen uptake capacity and plateau pressure of Pd/Al2O3 composite remain unchanged, and the hydrogen absorption rate increases slightly. No palladium particle pulverization or alumina ball rupture is observed. Pd/Al2O3 composite exhibits excellent anti-pulverization performance and has the potential of application in hydrogen isotope separation.
